U.S. patent application number 11/532726 was filed with the patent office on 2007-04-26 for malfunction detection via pressure pulsation.
This patent application is currently assigned to LifeScan, Inc.. Invention is credited to Deon Anex, Sebastian Bohm, Peter Krulevitch, Mingqi Zhao.
Application Number | 20070093753 11/532726 |
Document ID | / |
Family ID | 46045551 |
Filed Date | 2007-04-26 |
United States Patent
Application |
20070093753 |
Kind Code |
A1 |
Krulevitch; Peter ; et
al. |
April 26, 2007 |
Malfunction Detection Via Pressure Pulsation
Abstract
Systems and methods of detecting occlusions and fluid-loss
conditions (e.g., disconnects and/or leakages) in an infusion pump
are discussed. For example, electrokinetic infusion pumps may
develop an occlusion in the fluid flow path, which can disrupt
control of fluid dispersed from the pump. As well, an infusion set
disconnect can also result in a fluid-loss that can be disruptive.
Such disruptions can be troublesome to systems that control the
infusion pump, such as closed loop controllers. Accordingly,
systems and methods described herein can be used to detect such
occlusions and fluid-loss conditions during infusion pump
operation. For example, a position sensor can be used to monitor
fluid flow from the infusion pump, with the measurement being
compared with an expected value to detect an occlusion or
fluid-loss condition. Other algorithms for utilizing the position
sensor are also described.
Inventors: |
Krulevitch; Peter;
(Pleasanton, CA) ; Bohm; Sebastian; (Los Gatos,
CA) ; Zhao; Mingqi; (San Jose, CA) ; Anex;
Deon; (Livermore, CA) |
Correspondence
Address: |
NUTTER MCCLENNEN & FISH LLP
WORLD TRADE CENTER WEST
155 SEAPORT BOULEVARD
BOSTON
MA
02210-2604
US
|
Assignee: |
LifeScan, Inc.
Milpitas
CA
|
Family ID: |
46045551 |
Appl. No.: |
11/532726 |
Filed: |
September 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60718572 |
Sep 19, 2005 |
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60718397 |
Sep 19, 2005 |
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60718412 |
Sep 19, 2005 |
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60718577 |
Sep 19, 2005 |
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60718578 |
Sep 19, 2005 |
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60718364 |
Sep 19, 2005 |
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60718399 |
Sep 19, 2005 |
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60718400 |
Sep 19, 2005 |
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60718398 |
Sep 19, 2005 |
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60718289 |
Sep 19, 2005 |
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Current U.S.
Class: |
604/131 ;
604/891.1 |
Current CPC
Class: |
A61M 5/14248 20130101;
A61M 5/1452 20130101; A61M 2205/3317 20130101; A61M 2005/14513
20130101; A61M 2205/3389 20130101; A61M 5/14244 20130101; A61M
5/16831 20130101; A61M 5/172 20130101 |
Class at
Publication: |
604/131 ;
604/891.1 |
International
Class: |
A61M 37/00 20060101
A61M037/00; A61K 9/22 20060101 A61K009/22 |
Claims
1. A method for detecting a malfunction in an infusion pump having
a non-mechanically driven movable partition, comprising:
determining a first position of the movable partition of the
infusion pump using a position sensor disposed on the pump;
activating the infusion pump for a first pre-determined amount of
time to induce movement of the movable partition; de-activating the
infusion pump for a second pre-determined amount of time;
determining a second position of the movable partition using the
position sensor; calculating a measured displacement based on the
first and second positions of the movable partition; and comparing
the measured displacement to a pre-determined threshold value to
determine whether the infusion pump is malfunctioning.
2. The method of claim 1, wherein the pre-determined threshold
value is a minimum acceptable value for the measured displacement
of the movable partition.
3. The method of claim 2, wherein comparing the measured
displacement to the pre-determined threshold value further
comprises indicating the presence of an occlusion in the infusion
pump if the measured displacement is less than the pre-determined
threshold value.
4. The method of claim 3, further comprising: generating an alarm
if the presence of the occlusion is detected.
5. The method of claim 2, further comprising: repeating the steps
of the method as the movable partition proceeds through the
infusion pump.
6. The method of claim 5, wherein the steps of determining the
first position of the movable partition include equating the first
position of the movable partition with a previously measured
position of the movable partition.
7. The method of claim 1, wherein the pre-determined threshold
value is a maximum acceptable value for the measured displacement
of the movable partition.
8. The method of claim 7, wherein comparing the measured
displacement to the pre-determined threshold value further
comprises indicating the presence of a fluid-loss condition in the
infusion pump if the measured displacement is greater than the
pre-determined threshold value.
9. The method of claim 8, further comprising: generating an alarm
if the presence of the fluid-loss condition is detected.
10. The method of claim 7, further comprising: repeating the steps
of the method as the movable partition proceeds through the
infusion pump.
11. The method of claim 10, wherein the steps of determining the
first position of the movable partition include equating the first
position of the movable partition with a previously measured
position of the movable partition.
12. The method of claim 1, wherein determining the position of the
movable partition further comprises using a magnetic sensor.
13. The method of claim 1, wherein activating the infusion pump for
the first pre-determined amount of time is effective to cause a
pressure build up in the pump.
14. The method of claim 13, wherein de-activating the infusion pump
includes increasing the second pre-determined amount of time to
cause a larger drop in pressure in the pump.
15. The method of claim 13, wherein de-activating the infusion pump
includes decreasing the second pre-determined amount of time to
cause a smaller drop in pressure in the pump.
16. The method of claim 1, wherein calculating a measured
displacement comprises calculating a measured volume based on the
first and second positions of the movable partition.
17. The method of claim 1, wherein the infusion pump is an
electrokinetic infusion pump.
18. A system for detecting a malfunction in an infusion pump,
comprising: an infusion pump having a non-mechanically driven
movable partition disposed therein; a position sensor disposed on
the pump, wherein the position sensor comprises at least one of a
magnetic sensor, an optical sensor, and a linear variable
differential transformer; a controller associated with the infusion
pump and adapted to operate the infusion pump in an
activate/de-activate cycle, the cycle comprising activating the
pump for a first pre-determined amount of time to induce movement
of the movable partition and de-activating the pump for a second
pre-determined amount of time; and a processor associated with the
position sensor, the processor adapted to calculate a measured
displacement based on the first and second positions of the movable
partition, and to compare the measured displacement with a
pre-determined threshold value to determine whether the infusion
pump is malfunctioning.
19. The system of claim 18, wherein the controller is adapted cause
a pressure build up in the infusion pump, the pressure build up
being associated with the activation of the pump for the first
pre-determined amount of time.
20. The system of claim 18, wherein the pre-determined threshold
value is a minimum acceptable value for the measured
displacement.
21. The system of claim 20, wherein the processor is adapted to
indicate a presence of an occlusion in the infusion pump if the
measured displacement is less than the pre-determined threshold
value.
22. The system of claim 18, wherein the pre-determined threshold
value is a maximum acceptable value for the measured
displacement.
23. The system of claim 22, wherein the processor is adapted to
indicate a presence of a fluid-loss condition in the infusion pump
if the measured displacement is greater than the pre-determined
threshold value.
24. The system of claim 18, wherein the controller is further
adapted to repeat the activate/de-activate cycle while fluid is
being delivered by the infusion pump.
25. The system of claim 18, further comprising an alarm signal
generator coupled to the processor and configured to produce an
alarm signal if the processor determines that the infusion pump is
malfunctioning.
26. The system of claim 18, wherein the infusion pump is an
electrokinetic infusion pump.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of the following
U.S. Provisional Applications, all filed on Sep. 19, 2005: Ser. No.
60/718,572, bearing attorney docket number LFS-5093USPSP and
entitled "Electrokinetic Infusion Pump with Detachable Controller
and Method of Use"; Ser. No. 60/718,397, bearing attorney docket
number LFS-5094USPSP and entitled "A Method of Detecting Occlusions
in an Electrokinetic Pump Using a Position Sensor"; Ser. No.
60/718,412, bearing attorney docket number LFS-5095USPSP and
entitled "A Magnetic Sensor Capable of Measuring a Position at an
Increased Resolution"; Ser. No. 60/718,577, bearing attorney docket
number LFS-5096USPSP and entitled "A Drug Delivery Device Using a
Magnetic Position Sensor for Controlling a Dispense Rate or
Volume"; Ser. No. 60/718,578, bearing attorney docket number
LFS-5097USPSP and entitled "Syringe-Type Electrokinetic Infusion
Pump and Method of Use"; Ser. No. 60/718,364, bearing attorney
docket number LFS-5098USPSP and entitled "Syringe-Type
Electrokinetic Infusion Pump for Delivery of Therapeutic Agents";
Ser. No. 60/718,399, bearing attorney docket number LFS-5099USPSP
and entitled "Electrokinetic Syringe Pump with Manual Prime
Capability and Method of Use"; Ser. No. 60/718,400, bearing
attorney docket number LFS-5100USPSP and entitled "Electrokinetic
Pump Integrated within a Plunger of a Syringe Assembly"; Ser. No.
60/718,398, bearing attorney docket number LFS-5101USPSP and
entitled "Reduced Size Electrokinetic Pump Using an Indirect
Pumping Mechanism with Hydraulic Assembly"; and Ser. No.
60/718,289, bearing attorney docket number LFS-5102USPSP and
entitled "Manual Prime Capability of an Electrokinetic Syringe Pump
and Method of Use." The present application is also related to the
following applications, all filed currently herewith: "Infusion
Pump with Closed Loop Control and Algorithm" (Attorney Docket No.
106731-3), "Malfunction Detection With Derivative Calculation"
(Attorney Docket No. 106731-22), "Infusion Pumps with a Position
Sensor" (Attorney Docket No. 106731-18), "Systems and Methods for
Detecting a Partition Position in an Infusion Pump" (Attorney
Docket No. 106731-21), "Electrokinetic Infusion Pump System"
(Attorney Docket No. 106731-5). All of the applications recited in
this paragraph are hereby incorporated by reference herein in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates, in general, to medical
devices and systems and, in particular, to infusion pumps, infusion
pump systems and associated methods.
BACKGROUND OF THE INVENTION
[0003] Electrokinetic pumps provide for liquid displacement by
applying an electric potential across a porous dielectric media
that is filled with an ion-containing electrokinetic solution.
Properties of the porous dielectric media and ion-containing
solution (e.g., permittivity of the ion-containing solution and
zeta potential of the solid-liquid interface between the porous
dielectric media and the ion-containing solution) are predetermined
such that an electrical double-layer is formed at the solid-liquid
interface. Thereafter, ions of the electrokinetic solution within
the electrical double-layer migrate in response to the electric
potential, transporting the bulk electrokinetic solution with them
via viscous interaction. The resulting electrokinetic flow (also
known as electroosmotic flow) of the bulk electrokinetic solution
is employed to displace (i.e., "pump") a liquid. Further details
regarding electrokinetic pumps, including materials, designs, and
methods of manufacturing are included in U.S. patent application
Ser. No. 10/322,083 filed on Dec. 17, 2002, which is hereby
incorporated in full by reference.
SUMMARY OF THE INVENTION
[0004] One exemplary embodiment is directed to a method of
detecting a malfunction in an infusion pump using a pressure
pulsation technique. Generally, the malfunction detection method
can include determining a first position of a movable partition of
an infusion pump having a non-mechanically driven movable
partition, activating the infusion pump for a first pre-determined
amount of time to induce movement of the movable partition,
de-activating the infusion pump for a second predetermined amount
of time, determining a second position of the movable partition,
calculating a measured displacement based on the first and second
positions of the movable partition, and comparing the measured
displacement to a pre-determined threshold value to determine
whether the infusion pump is malfunctioning. In one exemplary
embodiment, the infusion pump can be an electrokinetic infusion
pump. The position of the movable partition can be determined using
a magnetic sensor. Calculating the measured displacement can
include calculating a measured volume based on the first and second
positions of the movable partition. Further, the pre-determined
threshold value can represent a variety of infusion pump operating
parameters.
[0005] In one embodiment, the pre-determined threshold value can be
a minimum acceptable value of the measured displacement of the
movable partition. In this embodiment, the step of comparing the
measured displacement to the predetermined value can further
include indicating the presence of an occlusion in the pump if the
measured displacement is less than the pre-determined threshold
value. The malfunction detection method can also include repeating
the steps of the method as the movable partition proceeds through
the infusion pump. In this embodiment, the step of determining the
first position of the movable partition can include equating the
first position of the movable partition with a previously measured
position of the movable partition. The method can also include
generating an alarm if the presence of an occlusion is
detected.
[0006] In another embodiment, the pre-determined threshold value
can be a maximum acceptable value of the measured displacement of
the movable partition. In this embodiment, the step of comparing
the measured displacement to the pre-determined value can further
include indicating the presence of a fluid-loss condition in the
pump if the measured displacement is greater than the
pre-determined threshold value. As with the occlusion detection
method, the fluid-loss detection method can also include repeating
the steps of the method as the movable partition proceeds through
the infusion pump. In this embodiment, the step of determining the
first position of the movable partition can include equating the
first position of the movable partition with a previously measured
position of the movable partition. The method can also include
generating an alarm if the presence of a fluid-loss condition is
detected.
[0007] In another exemplary embodiment of the malfunction detection
method, the step of activating the infusion pump for the first
pre-determined amount of time can be effective to cause a pressure
build up in the pump. In this embodiment, de-activating the pump
can include increasing the second pre-determined amount of time to
cause a larger pressure drop in the pump. The second pre-determined
amount of time can also be decreased to cause a smaller pressure
drop in the pump.
[0008] A system for detecting a malfunction in an infusion pump is
also provided. The system can include an infusion pump having a
non-mechanically driven movable partition disposed therein, a
position sensor disposed on the pump, a controller associated with
the pump, and a processor associated with the position sensor. A
variety of configurations are available for the position sensor.
For example, the position sensor can be a magnetic sensor, an
optical sensor, or a linear variable differential transformer. In
one embodiment, the infusion pump can be an electrokinetic infusion
pump. The controller can be adapted to operate the infusion pump in
an activate/de-activate cycle. The cycle can include activating the
pump for a first predetermined amount of time to induce movement of
the movable partition and de-activating the pump for a second
pre-determined amount of time. In one embodiment, the controller
can be adapted to cause a pressure build up in the infusion pump.
In this embodiment, the pressure build up can be associated with
the activation of the pump for the first pre-determined amount of
time. The processor can be adapted to calculate a measured
displacement based on the first and second positions of the movable
partition, and to compare the measured displacement with a
pre-determined threshold value to determine whether the infusion
pump is malfunctioning.
[0009] In one embodiment, the pre-determined threshold value can be
a minimum acceptable value for the measured displacement. In this
embodiment, the processor can be adapted to indicate a presence of
an occlusion in the infusion pump if the measured displacement is
less than the pre-determined threshold value. In another exemplary
embodiment, the pre-determined threshold value can be a maximum
acceptable value for the measured displacement. In this embodiment,
the processor can be adapted to indicate presence of a fluid-loss
condition in the infusion pump if the measured displacement is
greater than the pre-determined threshold value.
[0010] In another embodiment, the controller can be further adapted
to repeat the activate/de-activate cycle while fluid is being
delivered by the infusion pump. The malfunction detection system
can also include an alarm signal generator that is coupled to the
processor and configured to produce an alarm signal if the
processor determines that the infusion pump is malfunctioning.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention will be more fully understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0012] FIG. 1A is a schematic illustration of an electrokinetic
pump in a first dispense position consistent with an embodiment of
the invention, the pump including an electrokinetic engine, an
infusion module, and a closed loop controller.
[0013] FIG. 1B is a schematic illustration of the electrokinetic
pump of FIG. 1A in a second dispense position.
[0014] FIG. 2 is flow sheet illustrating a closed loop control
algorithm for use with an electrokinetic infusion pump with closed
loop control, according to an embodiment of the present
invention.
[0015] FIG. 3 is an illustration of an electrokinetic infusion pump
with closed loop control according to an additional embodiment of
the present invention.
[0016] FIG. 4 is an illustration of a magnetic linear position
detector as can be used in an electrokinetic infusion pump with
closed loop control according to an embodiment of the present
invention.
[0017] FIGS. 5A and 5B illustrate portions of an electrokinetic
infusion pump with closed loop control according to an embodiment
of the present invention, including an electrokinetic engine, an
infusion module, a magnetostrictive waveguide, and a position
sensor control circuit. The electrokinetic infusion pump with
closed loop control illustrated in FIG. 5A is in a first dispense
position, while the electrokinetic infusion pump with closed loop
control illustrated in FIG. 5B is in a second dispense
position.
[0018] FIG. 6 is a block diagram of a sensor signal processing
circuit that can be used in an electrokinetic infusion pump with
closed loop control according to an additional embodiment of the
present invention. The block diagram illustrated in FIG. 6 includes
a microprocessor, a digital to analog converter, an analog to
digital converter, a voltage nulling device, a voltage amplifier, a
position sensor control circuit, a magnetostrictive waveguide, and
an electrokinetic infusion pump.
[0019] FIG. 7 is an illustration of an electrokinetic infusion pump
with closed loop control according to an embodiment of the present
invention. The electrokinetic infusion pump with closed loop
control illustrated in FIG. 7 includes an electrokinetic engine and
infusion module, and was used to generate basal and bolus delivery
of infusion liquid.
[0020] FIG. 8 is a graph showing the performance of the
electrokinetic infusion pump with closed loop control illustrated
in FIG. 7 in both basal and bolus modes.
[0021] FIG. 9 is a flow diagram illustrating a method of detecting
occlusions in an electrokinetic infusion pump with closed loop
control according to an additional embodiment of the present
invention.
[0022] FIG. 10 is a graph illustrating back pressure in an
electrokinetic infusion pump with closed loop control according to
an embodiment of the present invention.
[0023] FIG. 11 is a graph illustrating the position of a moveable
partition as a function of time when an occlusion occurs in an
electrokinetic infusion pump with closed loop control according to
an embodiment of the present invention.
[0024] FIG. 12 is a graph illustrating sensor counts and shot
duration as a function of time when an occlusion occurs in a
electrokinetic infusion pump with closed loop control according to
an embodiment of the present invention.
[0025] FIG. 13 is graph illustrating the moving average over the
course of a series of shots when an occlusion occurs in a
electrokinetic infusion pump with closed loop control according to
an embodiment of the present invention.
[0026] FIG. 14 is a graph illustrating the number of false alarms
for various values of first pre-determined threshold values.
[0027] FIG. 15 is a graph illustrating sensor counts and shot
duration as a function of time when a disconnect occurs in a
electrokinetic infusion pump with closed loop control according to
an embodiment of the present invention.
[0028] FIG. 16 is a flow sheet illustrating a malfunction detection
algorithm for use with an electrokinetic infusion pump with closed
loop control, according to an embodiment of the present
invention.
[0029] FIG. 16A is a flow sheet illustrating one embodiment of the
malfunction detection algorithm shown in FIG. 16.
[0030] FIG. 16B is a flow sheet illustrating another embodiment of
the malfunction detection algorithm shown in FIG. 16.
[0031] FIG. 17 is a flow sheet illustrating another malfunction
detection algorithm for use with an electrokinetic infusion pump
with closed loop control, according to an embodiment of the present
invention.
[0032] FIG. 17A is a flow sheet illustrating one embodiment of the
malfunction detection algorithm shown in FIG. 17.
[0033] FIG. 17B is a flow sheet illustrating another embodiment of
the malfunction detection algorithm shown in FIG. 17.
[0034] FIG. 18 illustrates a malfunction detection system according
to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Certain exemplary embodiments will now be described to
provide an overall understanding of the principles of the
structure, function, manufacture, and use of the devices and
methods disclosed herein. One or more examples of these embodiments
are illustrated in the accompanying drawings. Those of ordinary
skill in the art will understand that the devices and methods
specifically described herein and illustrated in the accompanying
drawings are non-limiting exemplary embodiments and that the scope
of the present invention is defined solely by the claims. The
features illustrated or described in connection with one exemplary
embodiment may be combined with the features of other embodiments.
Such modifications and variations are intended to be included
within the scope of the present invention.
[0036] Embodiments of the present invention generally provide
methods and systems for detecting malfunctions in infusion pumps. A
variety of malfunctions are associated with the operation of
infusion pumps. For example, occlusions, bubbles or other
obstructions that form in an infusion set, can interfere with the
flow from an infusion pump and result in inaccurate doses of
infusion fluid. Other potential issues with infusion pumps include
disconnects within the infusion set and leaks. The malfunction
detection methods disclosed herein can include determining a first
position of a movable partition of an infusion pump, activating the
infusion pump to induce movement of the movable partition,
de-activating the infusion pump, determining a second position of
the movable partition, calculating a measured displacement based on
the first and second positions of the movable partition, and
comparing the measured displacement to pre-determined threshold
value to determine whether the infusion pump is malfunctioning. The
methods for detecting malfunctions in infusion pumps provided
herein can work in conjunction with a variety of infusion pumps
including, but not limited to, electrokinetic infusion pumps with
closed loop control. Select embodiments of exemplary electrokinetic
infusion pump systems are described below. Further details
regarding infusion pumps with closed loop control suitable for use
with the malfunction detection methods of the present invention are
included co-pending applications entitled "Infusion Pump with
Closed Loop Control and Algorithm" (Attorney Docket No. 106731-3)
and "Electrokinetic Infusion Pump System" (Attorney Docket No.
106731-5), filed concurrently herewith and hereby incorporated by
reference in their entirety.
[0037] Electrokinetic Infusion Pumps
[0038] Electrokinetic pumping can provide the driving force for
displacing infusion liquid. Electrokinetic pumping (also known as
electroosmotic flow) works by applying an electric potential across
an electrokinetic porous media that is filled with electrokinetic
solution. Ions in the electrokinetic solution form double layers in
the pores of the electrokinetic porous media, countering charges on
the surface of the electrokinetic porous media. Ions migrate in
response to the electric potential, dragging the bulk
electrokinetic solution with them. Electrokinetic pumping can be
direct or indirect, depending upon the design. In direct pumping,
infusion liquid is in direct contact with the electrokinetic porous
media, and is in direct electrical contact with the electrical
potential. In indirect pumping, infusion liquid is separated from
the electrokinetic porous media and the electrokinetic solution by
way of a moveable partition. Further details regarding
electrokinetic pumps, including materials, designs, and methods of
manufacturing, suitable for use in devices according to the present
invention are included in U.S. patent application Ser. No.
10/322,083 filed on Dec. 17, 2002, and Ser. No. 11/112,867 filed on
Apr. 21, 2005, which are hereby incorporated by reference in their
entirety.
[0039] A variety of infusion liquids can be delivered with
electrokinetic infusion pumps using closed loop control, including
insulin for diabetes; morphine and/or other analgesics for pain;
barbiturates and ketamine for anesthesia; anti-infective and
antiviral therapies for AIDS; antibiotic therapies for preventing
infection; bone marrow for immunodeficiency disorders, blood-borne
malignancies, and solid tumors; chemotherapy for cancer; and
dobutamine for congestive heart failure. The electrokinetic
infusion pumps with closed loop control can also be used to deliver
biopharmaceuticals. Biopharmaceuticals are difficult to administer
orally due to poor stability in the gastrointestinal system and
poor absorption. Biopharmaceuticals that can be delivered include
monoclonal antibodies and vaccines for cancer, BNP-32 (Natrecor)
for congestive heart failure, and VEGF-121 for preeclampsia. The
electrokinetic infusion pumps with closed loop control can deliver
infusion liquids to the patient in a number of ways, including
subcutaneously, intravenously, or intraspinally. For example, the
electrokinetic infusion pumps can deliver insulin subcutaneously as
a treatment for diabetes, or can deliver stem cells and/or
sirolimus to the adventitial layer in the heart via a catheter as a
treatment for cardiovascular disease.
[0040] FIGS. 1A and 1B are schematic illustrations of an
electrokinetic infusion pump with closed loop control 100 in accord
with an exemplary embodiment. The electrokinetic infusion pump
system illustrated in FIGS. 1A and 1B includes an electrokinetic
infusion pump 103, and a closed loop controller 105. The
electrokinetic infusion pump illustrated in FIG. 1A is in a first
dispense position, while the pump illustrated in FIG. 1B is in a
second dispense position. Electrokinetic infusion pump 103 includes
electrokinetic engine 102 and infusion module 104. Electrokinetic
engine 102 includes electrokinetic supply reservoir 106,
electrokinetic porous media 108, electrokinetic solution receiving
chamber 118, first electrode 110, second electrode 112, and
electrokinetic solution 114. Closed loop controller 105 includes
voltage source 115, and controls electrokinetic engine 102.
Infusion module 104 includes infusion housing 116, electrokinetic
solution receiving chamber 118, movable partition 120, infusion
reservoir 122, infusion reservoir outlet 123, and infusion liquid
124. In operation, electrokinetic engine 102 provides the driving
force for displacing infusion liquid 124 from infusion module 104.
During fabrication, electrokinetic supply reservoir 106,
electrokinetic porous media 108, and electrokinetic solution
receiving chamber 118 are filled with electrokinetic solution 114.
Before use, the majority of electrokinetic solution 114 is in
electrokinetic supply reservoir 106, with a small amount in
electrokinetic porous media 108 and electrokinetic solution
receiving chamber 118. To displace infusion liquid 124, a voltage
is established across electrokinetic porous media 108 by applying
potential across first electrode 110 and second electrode 112. This
causes electrokinetic pumping of electrokinetic solution 114 from
electrokinetic supply reservoir 106, through electrokinetic porous
media 108, and into electrokinetic solution receiving chamber 118.
As electrokinetic solution receiving chamber 118 receives
electrokinetic solution 114, pressure in electrokinetic solution
receiving chamber 118 increases, forcing moveable partition 120 in
the direction of arrows 127, i.e., the partition 120 is
non-mechanically-driven. As moveable partition 120 moves in the
direction of arrows 127, it forces infusion liquid 124 out of
infusion reservoir outlet 123. Electrokinetic engine 102 continues
to pump electrokinetic solution 114 until moveable partition 120
reaches the end nearest infusion reservoir outlet 123, displacing
nearly all infusion liquid 124 from infusion reservoir 122.
[0041] Once again referring to the electrokinetic infusion pump
with closed loop control 100 illustrated in FIGS. 1A and 1B, the
rate of displacement of infusion liquid 124 from infusion reservoir
122 is directly proportional to the rate at which electrokinetic
solution 114 is pumped from electrokinetic supply reservoir 106 to
electrokinetic solution receiving chamber 118. The rate at which
electrokinetic solution 114 is pumped from electrokinetic supply
reservoir 106 to electrokinetic solution receiving chamber 118 is a
function of the voltage and current applied across first electrode
110 and second electrode 112. It is also a function of the physical
properties of electrokinetic porous media 108 and the physical
properties of electrokinetic solution 114. As mentioned previously,
further details regarding electrokinetic pumps, including
materials, designs, and methods of manufacturing, suitable for use
in devices according to the present invention are included in U.S.
patent application Ser. No. 10/322,083 filed on Dec. 17, 2002,
which has been incorporated by reference in its entirety.
[0042] In FIG. 1A, movable partition 120 is in first position 119,
while in FIG. 1B, movable partition 120 is in second position 121.
The position of movable partition 120 can be determined, and used
by closed loop controller 105 to control the voltage and current
applied across first electrode 110 and second electrode 112. By
controlling the voltage and current applied across first electrode
110 and second electrode 112, the rate at which electrokinetic
solution 114 is pumped from electrokinetic supply reservoir 106 to
electrokinetic solution receiving chamber 118 and the rate at which
infusion liquid 124 is pumped through infusion reservoir outlet 123
can be controlled. A closed loop controller can use the position of
movable partition 120 to control the voltage and current applied to
first electrode 110 and second electrode 112, and accordingly
control infusion fluid delivered from the electrokinetic infusion
pump.
[0043] The position of movable partition 120 can be determined
using a variety of techniques. In some embodiments, movable
partition 120 can include a magnet, and a magnetic sensor can be
used to determine its position. FIG. 4 illustrates the principles
of one particular magnetic position sensor 176. Magnetic position
sensor 176, suitable for use in this invention, can be purchased
from MTS Systems Corporation, Sensors Division, of Cary, N.C. In
magnetic position sensor 176, a sonic strain pulse is induced in
magnetostrictive waveguide 177 by the momentary interaction of two
magnetic fields. First magnetic field 178 is generated by movable
permanent magnet 149 as it passes along the outside of
magnetostrictive waveguide 177. Second magnetic field 180 is
generated by current pulse 179 as it travels down magnetostrictive
waveguide 177. The interaction of first magnetic field 178 and
second magnetic field 180 creates a strain pulse. The strain pulse
travels, at sonic speed, along magnetostrictive waveguide 177 until
the strain pulse is detected by strain pulse detector 182. The
position of movable permanent magnet 149 is determined by measuring
the elapsed time between application of current pulse 179 and
detection of the strain pulse at strain pulse detector 182. The
elapsed time between application of current pulse 179 and arrival
of the resulting strain pulse at strain pulse detector 182 can be
correlated to the position of movable permanent magnet 149.
[0044] Other types of position detectors that include a magnetic
sensor for identifying the position of a moveable partition that
use a magnetic sensor can also be used such as Hall-Effect sensors.
In a particular example, anisotropic magnetic resistive sensors can
be advantageously used with infusion pumps, as described in the
co-pending application entitled "Infusion Pumps with a Position
Sensor" (Attorney Docket No. 106731-18), filed concurrently
herewith and hereby incorporated herein by reference in its
entirety. In other embodiments, optical components can be used to
determine the position of a movable partition. Light emitters and
photodetectors can be placed adjacent to an infusion housing, and
the position of the movable partition determined by measuring
variations in detected light. In still other embodiments, a linear
variable differential transformer (LVDT) can be used. In
embodiments where an LVDT is used, the moveable partition includes
an armature made of magnetic material. A LVDT that is suitable for
use in the present application can be purchased from RDP
Electrosense Inc., of Pottstown, Pa. Those skilled in the art will
appreciate that other types of position detectors can also be
utilized, consistent with embodiments of the present invention.
[0045] Depending upon desired end use, electrokinetic engine 102
and infusion module 104 can be integrated into a single assembly,
or can be separate and connected by tubing. Electrokinetic engine
102 and infusion module 104 illustrated in FIGS. 3, 5A, and 5B are
integrated, while electrokinetic engine 102 and infusion module 104
illustrated in FIG. 8 are not integrated. Regardless of whether
electrokinetic engine 102 and infusion module 104 are integrated,
the position of movable partition 120 can be measured, and used to
control the voltage and current applied across electrokinetic
porous media 108. In this way, electrokinetic solution 114 and
infusion liquid 124 can be delivered consistently in either an
integrated or separate configuration.
[0046] Electrokinetic supply reservoir 106, as used in the
electrokinetic infusion pump with closed loop control illustrated
in FIGS. 1A, 1B, 3, 5A, 5B, 7 and 8, can be collapsible, at least
in part. This allows the size of electrokinetic supply reservoir
106 to decrease as electrokinetic solution 114 is removed.
Electrokinetic supply reservoir 106 can be constructed using a
collapsible sack, or can include a moveable piston with seals.
Also, infusion housing 116, as used in electrokinetic infusion pump
with closed loop control in FIGS. 1A, 1B, 3, 5A, 5B, 7, and 8, is
preferably rigid, at least in part. This makes it easier to
displace moveable partition 120 than to expand infusion housing 116
as electrokinetic solution receiving chamber 118 receives
electrokinetic solution 114 pumped from electrokinetic supply
reservoir 106, and can provide more precise delivery of infusion
liquid 124. Moveable partition 120 can be designed to prevent
migration of electrokinetic solution 114 into infusion liquid 124,
while decreasing resistance to displacement as electrokinetic
solution receiving chamber 118 receives electrokinetic solution 114
pumped from electrokinetic supply reservoir 106. In some
embodiments, moveable partition 120 includes elastomeric seals that
provide intimate yet movable contact between moveable partition 120
and infusion housing 116. In some embodiments, moveable partition
120 is piston-like, while in other embodiments moveable partition
120 is fabricated using membranes and/or bellows. As mentioned
previously, closed loop control can help maintain consistent
delivery of electrokinetic solution 114 and infusion liquid 124, in
spite of variations in resistance caused by variations in the
volume of electrokinetic supply reservoir 106, by variations in the
diameter of infusion housing 116, and/or by variations in back
pressure at the user's infusion site.
[0047] Closed Loop Control Schemes
[0048] Various exemplary embodiments are directed to methods and
systems for controlling the delivery of infusion liquids from an
electrokinetic infusion pump. In particular embodiments, a closed
loop control scheme can be utilized to control delivery of the
infusion liquid. Although many of the various closed loop control
schemes described in the present application are described in the
context of their use with electrokinetic engines, embodiments using
other engines are also within the scope of embodiments of the
present invention. Closed loop control, as described in the present
application, can be useful in many types of infusion pumps. These
include pumps that use engines or driving mechanisms that generate
pressure pulses in a hydraulic medium in contact with the movable
partition in order to induce partition movement. These driving
mechanisms can be based on gas generation, thermal
expansion/contraction, and expanding gels and polymers, used alone
or in combination with electrokinetic engines. As well, engines in
infusion pumps that utilize a moveable partition to drive delivery
an infusion fluid (e.g., non-mechanically driven partitions of an
infusion pump such as hydraulically actuated positions) can include
the closed loop control schemes described herein. Further details
regarding electrokinetic infusion pumps with closed loop control
suitable for use with the malfunction detection methods of the
present invention are included in co-pending application entitled
"Infusion Pump with Closed Loop Control and Algorithm" (Attorney
Docket No. 106731-3) filed concurrently herewith and hereby
incorporated by reference in its entirety.
[0049] Use of a closed loop control scheme with an electrokinetic
infusion pump can compensate for variations that may cause
inconsistent dispensing of infusion liquid. For example, with
respect to FIGS. 1A and 1B, if flow of electrokinetic solution 114
varies as a function of the temperature of electrokinetic porous
media 108, variations in the flow of infusion liquid 124 can occur
if a constant voltage is applied across first electrode 110 and
second electrode 112. By using closed loop control, the voltage
across first electrode 110 and second electrode 112 can be varied
based upon the position of movable partition 120 and the desired
flow of infusion liquid 124. Another example of using closed loop
control involves compensating for variations in flow caused by
variations in down stream resistance to flow. In cases where there
is minimal resistance to flow, lower voltages and current may be
used to achieve a desired flow of electrokinetic solution 114 and
infusion liquid 124. In cases where there is higher resistance to
flow, higher voltages and current may be used to achieve a desired
flow of electrokinetic solution 114 and infusion liquid 124. Since
resistance to flow is often unknown and/or changing, variations in
flow of electrokinetic solution 114 and infusion liquid 124 may
result. By determining the position of movable partition 120, the
current and voltage can be adjusted to deliver a desired flow rate
of electrokinetic solution 114 and infusion liquid 124, even if the
resistance to flow is changing. Another example of using closed
loop control involves compensating for variation in flow caused by
variation in the force required to push movable partition 120.
Variations in friction between movable partition 120 and the inside
surface of infusion housing 116 may cause variations in the force
required to push movable partition 120. If a constant voltage and
current are applied across electrokinetic porous media 108,
variation in flow of electrokinetic solution 114 and infusion
liquid 124 may result. By monitoring the position of movable
partition 120, and varying the voltage and current applied across
electrokinetic porous media 108, a desired flow rate of
electrokinetic solution 114 and infusion liquid 124 can be
achieved. Accordingly, in some embodiments, a closed loop control
algorithm can utilize a correction factor, as discussed herein, to
alter operation of a pump (e.g., using the correction factor to
change the current and/or voltage applied across the electrokinetic
pump's electrodes).
[0050] Electrokinetic infusion pumps that utilize a closed loop
control scheme can operate in a variety of manners. For example,
the pump can be configured to deliver a fluid shot amount in a
continuous manner (e.g., maintaining a constant flow rate) by
maintaining one or more pump operational parameters at a constant
value. Non-limiting examples include flow rate of infusion fluid or
electrokinetic solution, pressure, voltage or current across
electrodes, and power output from a power source. In such
instances, a closed loop control scheme can be used to control the
operational parameter at or near the desired value.
[0051] In some embodiments, the pump is configured to deliver an
infusion fluid by delivering a plurality of fluid shot amounts. For
example, the electrokinetic infusion pump can be configured to be
activated to deliver a shot amount of fluid. The amount can be
determined using a variety of criteria such as a selected quantity
of fluid or application of a selected voltage and/or current across
the electrodes of the pump for a selected period of time. Following
activation, the pump can be deactivated for a selected period of
time, or until some operating parameter reaches a selected value
(e.g., pressure in a chamber of the electrokinetic pump).
Continuous cycles of activation/deactivation can be repeated, with
each cycle delivering one of the fluid shot amounts. An example of
such operation is discussed herein. Closed loop control schemes can
alter one or more of the parameters discussed with respect to an
activation/deactivation cycle to control delivery of the infusion
fluid. For instance, the shot duration of each shot can be altered
such that a selected delivery rate of infusion fluid from the pump
is achieved over a plurality of activation/deactivation cycles.
Alteration of shot durations during activation/deactivation cycles
can be utilized advantageously for the delivery of particular
infusion fluids such as insulin. For example, diabetic patients
typically receive insulin in two modes: a bolus mode where a
relatively large amount of insulin can be dosed (e.g., just before
a patient ingests a meal), and a basal mode where a relatively
smaller, constant level of insulin is dosed to maintain nominal
glucose levels in the patient. By utilizing activation/deactivation
cycles, both delivery modes can easily be accommodated by simply
adjusting the shot duration (e.g., very short shots during basal
delivery and one or more longer shots for a bolus delivery) and/or
the deactivation duration.
[0052] One potential advantage to operating under repeated
activation/deactivation cycles is that such an operation prevents
too much infusion fluid from being released at once. Take, for
example, an infusion pump operating at a constant delivery rate
(i.e., not a continuous activation/deactivation cycle). If such an
infusion pump becomes occluded, a closed loop controller could
potentially continue to try and advance the plunger, causing the
pressure to rise in the infusion set with little change in fluid
delivery. Thus, if the occlusion is suddenly removed, the stored
pressure could inject a potentially hazardous and even lethal dose
of infusion fluid into the patient. Electrokinetic infusion pumps
operating under a repeated cycle of activation and deactivation can
reduce the risk of overdose by allowing the pressure stored within
the infusion set to decrease over time due to leakage back through
the electrokinetic porous material. Accordingly, some of the
embodiments discussed herein utilize an infusion pump operating
with an activation/deactivation cycle.
[0053] Another potential advantage of utilizing continuous
activation/deactivation cycles is that such cycles can help an
electrokinetic pump avoid potential mechanical inefficiencies. For
example, with respect to insulin delivery in the basal mode, a very
small pressure may be associated with infusing insulin at a slow
rate. Very low pressures, however, may result in mechanical
inefficiencies with pump movement. For example, smooth
partition/piston movement may require a threshold pressure that
exceeds the low pressure needed to infuse insulin at the designated
basal rate, otherwise sporadic movement may result, leading to
difficulties in pump control. By utilizing activation/deactivation
cycles, a series of relatively small "microboluses" can be
released, sufficiently spaced in time, to act as a virtual basal
delivery. Each microbolus can use a high enough pressure to avoid
the mechanical inefficiencies.
[0054] Some embodiments are directed to methods of controlling
fluid delivery from an electrokinetic infusion pump. The
electrokinetic infusion pump can be configured to deliver one or
more fluid shot amounts. For example, the pump can deliver a single
continuous fluid shot amount, consistent with continuous operation.
Alternatively, a plurality of fluid shot amounts can be delivered
as in a series of activation/deactivation cycles. One or more
measured amounts can be determined for the plurality of shot
amounts. For example, a measured amount can be obtained for each of
a plurality of fluid shots, or after a selected number of fluid
shots when a pump operates utilizing a series of
activation/deactivation cycles. In another example, a series of
measured amounts can be determined for a single continuous shot,
corresponding to determining the amount of fluid displaced from the
pump over a series of given time intervals during continuous fluid
dispensing. Fluid shot amounts and measured amounts can be
described by a variety of quantities that denote an amount of
fluid. Though volume is utilized as a unit of shot amount in some
embodiments, non-limiting other examples include mass, a length
(e.g., with an assumption of some cross-sectional area), or a rate
(e.g., volumetric flow rate, flux, etc.). An average measured
amount can be calculated from the measured amounts, and
subsequently used to calculate a correction factor. The correction
factor can also depend upon an expected amount, which is either
selected by a pump user or designated by a processor or controller
of the pump. The correction factor can be used to adjust subsequent
fluid delivery from the pump (e.g., used to adjust a subsequent
fluid shot amount from the pump). Such subsequent fluid delivery
can be used to correct for previous over-delivery or under-delivery
of infusion fluid, or to deliver the expected amount.
[0055] During pump operation, as fluid is delivered, the steps of
determining a measured amount; calculating an average measured
amount; calculating a correction factor; and adjusting subsequent
fluid delivery based at least in part on the correction factor, can
be serially repeated (e.g., after each fluid shot, or after a
selected plurality of fluid shots when using
activation/deactivation cycles) to control dispensing of fluid from
the pump. A more specific example of the implementation of these
methods is described with respect to FIG. 2 herein.
[0056] FIG. 2 is a flow sheet illustrating a closed loop control
algorithm 400 for use with an electrokinetic infusion pump having
closed loop control, according to an embodiment of the present
invention. The immediate following description herein assumes that
the pump utilizes activation/deactivation cycles. Accordingly
measured amounts are referred to as measured shot amounts, average
measured amounts are referred to as average shot amounts, and
expected amounts are referred to as expected shot amounts. It is
understood, however, that the embodiment can also be utilized with
a pump operating in a continuous delivery mode as described
below.
[0057] With reference to FIGS. 1A, 1B, and 2, closed loop control
algorithm 400 starts with an initial shot profile 402, i.e.,
activation of the electrokinetic pump to cause a shot of infusion
fluid to be dispersed therefrom. The shot profile can be chosen to
provide an expected shot fluid amount to be dispensed from the
pump. In one example, shot profile 402 includes application of
voltage across first electrode 110 and second electrode 112 for a
selected length of time. The voltage is referred to as shot
voltage, and the time is referred to as shot duration. Although one
can vary shot voltage or shot duration (among other operational
variables) in closed loop control algorithms, in this description,
shot duration is varied.
[0058] Returning to FIG. 2, in shot profile 402, shot voltage is
applied for a shot duration, resulting in a delivered amount
intended to correspond with an expected shot amount. In one
particular example, shot amounts are designated by volume.
Therefore, the expected shot amount is an expected shot volume 404.
Next a corresponding measured shot volume 406 is measured. The
measured shot volume can be identified by any number of techniques.
For example, by measuring the displacement of movable partition 120
during a shot profile, and knowing the cross-sectional area of a
fluid reservoir, measured shot volume 406 can be determined. The
displacement of the moveable partition can be determined using any
number of position sensors, including those described herein.
[0059] When a position sensor is implemented, the particular
technique used to measure the position of movable partition 120 can
have a direct effect upon the precision and accuracy of measured
shot volume 406, and, accordingly, upon closed loop control
algorithm 400. In particular, if sampling of a position sensor's
movement between shots is such that the actual displacement is of
the order of the resolution of the position sensor, shot-to-shot
precision can be difficult to maintain with a closed loop control
scheme that only utilizes the last two measured shot amounts to
calculate a correction factor. Other sources of error can also
adversely affect the shot-to-shot precision (e.g., either random
errors or systematic errors that cause a drift in an operating
parameter such as fluid output over a period of time). To improve
the precision and accuracy of closed loop control algorithm 400,
measured shot volume 406 can be combined with previous measurements
to calculate an average measured shot volume 408, which can be used
in the closed loop control algorithm 400.
[0060] Returning to FIG. 2, the deviation from expected shot volume
410 can be determined by comparing the average measured shot volume
408 to the expected shot volume 404. The deviation from expected
shot volume 410 can then be used to calculate a correction factor
412, which can be applied to adjust a subsequent shot profile 402.
In this embodiment, the correction factor 412 is typically some
value indicative of the deviation between an expected shot amount
and an average shot amount. For example the correction factor 412
can be set equal to the deviation value. In another example, the
correction factor 412 can be the deviation multiplied by a
proportional adjustment such as a designated fraction, referred to
as .lamda., resulting in an adjusted correction factor 414. For
example, if .lamda.=0.4, then 40 percent of deviation is applied in
calculating the subsequent shot profile. Application of adjusted
correction factor 414 results in a subsequent shot profile 402, and
the algorithm is repeated, i.e., the adjusted correction factor is
used to determine some operating pump parameter such as voltage,
current, or shot duration to provide the subsequent shot
profile.
[0061] In one embodiment, several measured shot volumes are
determined and averaged before making corrections to shot profile
402. Henceforth, closed loop control algorithm 400 can be used to
adjust shot profile 402. Closed loop control algorithm 400 can be
particularly useful when electrokinetic infusion pump with closed
loop control 100 is delivering infusion liquid 124 in basal mode,
as is described in the Examples discussed below.
[0062] Electrokinetic Infusion Pump with Closed Loop Controller
[0063] FIG. 3 is an illustration of an electrokinetic infusion pump
with closed loop control 100 according to an exemplary embodiment
of the present invention. Electrokinetic infusion pump with closed
loop control 100 includes closed loop controller 105 and
electrokinetic infusion pump 103. In the embodiments of
electrokinetic infusion pump with closed loop control 100
illustrated in FIGS. 3, 5A, 5B, 7, and 8 electrokinetic infusion
pump 103 and closed loop controller 105 can be handheld, or mounted
to a user by way of clips, adhesives, or non-adhesive removable
fasteners. Closed loop controller 105 can be directly or wirelessly
connected to remote controllers that provide additional data
processing and/or analyte monitoring capabilities. As outlined
earlier, and referring to FIGS. 1 and 2, closed loop controller 105
and electrokinetic infusion pump 103 can include elements that
enable the position of movable partition 120 to be determined.
Closed loop controller 105 includes display 140, input keys 142,
and insertion port 156. After filling electrokinetic infusion pump
103 with infusion liquid 124, electrokinetic infusion pump 103 is
inserted into insertion port 156. Upon insertion into insertion
port 156, electrical contact is established between closed loop
controller 105 and electrokinetic infusion pump 103. An infusion
set is connected to the infusion reservoir outlet 123 after
electrokinetic infusion pump 103 is inserted into insertion port
156, or before it is inserted into insertion port 156. Various
means can be provided for priming of the infusion set, such as
manual displacement of moveable partition 120 towards infusion
reservoir outlet 123. After determining the position of moveable
partition 120, voltage and current are applied across
electrokinetic porous media 108, and infusion liquid 124 is
dispensed. Electrokinetic infusion pump with closed loop control
100 can be worn on a user's belt providing an ambulatory infusion
system. Display 140 can be used to display a variety of
information, including infusion rates, error messages, and logbook
information. Closed loop controller 105 can be designed to
communicate with other equipment, such as analyte measuring
equipment and computers, either wirelessly or by direct
connection.
[0064] FIGS. 5A and 5B illustrate portions of an electrokinetic
infusion pump with closed loop control according to an embodiment
of the present invention. FIGS. 5A and 5B include electrokinetic
infusion pump 103, closed loop controller 105, magnetic position
sensor 176, and position sensor control circuit 160. Position
sensor control circuit 160 is connected to closed loop controller
105 by way of feedback 138. Electrokinetic infusion pump 103
includes infusion housing 116, electrokinetic supply reservoir 106,
electrokinetic porous media 108, electrokinetic solution receiving
chamber 118, infusion reservoir 122, and moveable partition 120.
Moveable partition 120 includes first infusion seal 148, second
infusion seal 150, and moveable permanent magnet 149. Infusion
reservoir 122 is formed between moveable partition 120 and the
tapered end of infusion housing 116. Electrokinetic supply
reservoir 106, electrokinetic porous media 108, and electrokinetic
solution receiving chamber 118 contain electrokinetic solution 114,
while infusion reservoir 122 contains infusion liquid 124. Voltage
is controlled by closed loop controller 105, and is applied across
first electrode 110 and second electrode 112. Magnetic position
sensor 176 includes magnetostrictive waveguide 177, position sensor
control circuit 160, and strain pulse detector 182.
Magnetostrictive waveguide 177 and strain pulse detector 182 are
typically mounted on position sensor control circuit 160.
[0065] In FIG. 5A, moveable partition 120 is in first position 168.
Position sensor control circuit 160 sends a current pulse down
magnetostrictive waveguide 177, and by interaction of the magnetic
field created by the current pulse with the magnetic field created
by moveable permanent magnet 149, a strain pulse is generated and
detected by strain pulse detector 182. First position 168 can be
derived from the time between initiating the current pulse and
detecting the strain pulse. In FIG. 5B, electrokinetic solution 114
has been pumped from electrokinetic supply reservoir 106 to
electrokinetic solution receiving chamber 118, pushing moveable
partition 120 toward second position 172. Position sensor control
circuit 160 sends a current pulse down magnetostrictive waveguide
177, and by interaction of the magnetic field created by the
current pulse with the magnetic field created by moveable permanent
magnet 149, a strain pulse is generated and detected by strain
pulse detector 182. Second position 172 can be derived from the
time between initiating the current pulse and detecting the strain
pulse. Change in position 170 can be determined using the
difference between first position 168 and second position 172. As
mentioned previously, the position of moveable partition 120 can be
used in controlling flow in electrokinetic infusion pump 103.
[0066] As mentioned previously, when designing an electrokinetic
infusion pump with closed loop control 100, the infusion module 104
and the electrokinetic engine 102 can be integrated, as illustrated
in FIGS. 3, 5A, 5B, and 7, or they can be separate components
connected with tubing, as illustrated in FIG. 8. In FIG. 8,
electrokinetic infusion pump with closed loop control 100 includes
infusion module 104 and electrokinetic engine 102, connected by
connection tubing 244. Infusion module 104 includes moveable
partition 120 and infusion reservoir outlet 123. Moveable partition
120 includes moveable permanent magnet 149. Further details
regarding electrokinetic engine 102, including materials, designs,
and methods of manufacturing, suitable for use in electrokinetic
infusion pump with closed loop control 100 are included in U.S.
patent application Ser. No. 10/322,083, previously incorporated by
reference.
[0067] Malfunction Detection
[0068] As indicated above, electrokinetic infusion pumps can
operate in a variety of manners. For example, the pump can be
configured to deliver a fluid by maintaining some operational
parameter at a constant value. Non-limiting examples include flow
rate of infusion fluid or electrokinetic solution, pressure,
voltage or current across electrodes, and power output from a power
source. In some embodiments, the pump is configured to deliver an
infusion fluid by delivering a plurality of fluid shot amounts. For
example, the electrokinetic infusion pump can be configured to be
activated to deliver a shot amount of fluid. The amount can be
determined using a variety of criteria such as a selected quantity
of fluid (e.g., a microbolus of fluid) or application of a selected
voltage and/or current across the electrodes of the pump for a
selected period of time. Following activating, the pump can be
deactivated for a selected period of time, or until some operating
parameter reaches a selected value (e.g., pressure in a chamber of
the electrokinetic pump). Continuous cycles of
activation/deactivation can be repeated, with each cycle delivering
one of the fluid shot amounts.
[0069] One potential advantage to operating under the continuous
activation/deactivation cycle is that such an operation can prevent
too much infusion fluid from being released at once. Take, for
example, an infusion pump operating at a constant delivery rate
(i.e., not a continuous activation/deactivation cycle). If such an
infusion pump becomes occluded, the pump will continue to advance
the plunger, causing the pressure to rise in the infusion set, but
no infusion fluid will be delivered. Thus, if the occlusion is
suddenly removed, the stored pressure will inject a potentially
hazardous and even lethal dose of infusion fluid into the patient.
Electrokinetic infusion pumps operating under a continuous cycle of
activation and deactivation reduce the risk of overdose by allowing
the pressure stored within the infusion set to decrease over time
due to leakage back through the electrokinetic porous material.
FIG. 12 presents data from an electrokinetic infusion pump with
closed loop control that has become occluded. The sensor counts and
shot duration are shown as a function of time. As illustrated in
FIG. 12, the infusion set became blocked approximately 65 minutes
into the simulation. Blockage is indicated by a decrease in forward
plunger movement (reduced increase in sensor counts). As a result
of the plunger movement being smaller than a desired value, the
control algorithm tries to correct for this by increasing the shot
duration. Because the infusion set was occluded, the closed loop
controller was unable to correct the operation of the pump within
its operational boundaries. The following method for detecting
malfunctions provides an additional safeguard to electrokinetic
infusion pump operation.
[0070] Malfunction Detection with Microbolus Delivery
[0071] FIG. 16 is a flow diagram illustrating an exemplary
embodiment of a method of detecting malfunctions in an infusion
pump with closed loop control 100. Generally, the malfunction
detection method can include determining a first position of a
non-mechanically driven movable partition of an infusion pump 610,
activating the infusion pump to induce movement of the movable
partition 620, de-activating the infusion pump 630, determining a
second position of the movable partition 640, calculating a
measured displacement 650 based on the first and second positions
of the movable partition, and comparing the measured displacement
to a pre-determined threshold value to determine whether the
infusion pump is malfunctioning 660. Although the malfunction
detection methods are shown and described as applied to an infusion
pump having a closed loop control 100, a person skilled in the art
will appreciate that the malfunction detection methods disclosed
herein can be used with a variety of infusion pumps including
electrokinetic infusion pumps and those pumps without closed loop
control. Further, the malfunction detection methods disclosed
herein are independent of any particular closed loop control
algorithm and should not be limited to the closed loop control
embodiments specifically discussed herein.
[0072] As shown in FIGS. 1A and 1B, the position of the movable
partition 120 can be determined using a variety of techniques. For
example, a position sensor associated with the closed loop
controller 105 can be used to determine the position of the movable
partition 120. Exemplary position sensors include, but are not
limited to, magnetic position sensors, optical position sensors, or
linear variable differential transformers. In a particular example,
anisotropic magnetic resistive sensors can be advantageously used
with infusion pumps, as described in the co-pending application
entitled "Infusion Pumps with a Position Sensor" (Attorney Docket
No. 106731-18), filed concurrently herewith and hereby incorporated
herein by reference in its entirety. A person skilled in the art
will appreciate that any sensor capable of measuring position can
be used occlusion detection methods disclosed herein.
[0073] After determining the position 119 of the movable partition
120, the infusion pump can be activated for a first pre-determined
amount of time to induce movement of the movable partition 120. The
infusion pump can then be de-activated for a second pre-determined
amount of time, and a second position 121 of the movable partition
120 can be determined. As indicated above, activating the infusion
pump can include delivering a shot amount of fluid. The amount can
be determined using a variety of criteria such as a selected
quantity of fluid (e.g., a microbolus of fluid) or application of a
selected voltage and/or current across the electrodes of the pump
for a selected period of time. Following activation, the pump can
be deactivated for a selected period of time, or until some
operating parameter reaches a selected value (e.g., pressure in a
chamber of the pump). Deactivation can include reducing or
eliminating the voltage or current across the electrodes.
Activating and de-activating the infusion pump for the first and
second pre-determined amounts of time can affect the amount of
pressure in the pump and how long it takes for pressure to build up
in the pump. For example, activating the pump for the first
pre-determined amount of time can be effective to cause a pressure
build up in the pump such that the pressure build up is effective
to induce movement of the movable partition. De-activating the pump
can be effective reduce the amount of pressure in the pump. In one
embodiment, the infusion pump can be de-activated for a longer
period of time to cause a larger drop in pressure in the pump. In
another embodiment, the infusion pump can be de-activated for a
shorter period of time to cause a smaller drop in pressure in the
pump. Thus, the amount of pressure in the pump can be controlled by
increasing or decreasing the de-activation time. Continuous cycles
of activation/deactivation can be repeated, with each cycle
delivering one of the fluid shot amounts. Further, the infusion
pump can be activated and/or de-activated prior to determining the
position of the movable partition.
[0074] Once the first and second positions 119, 121 of the movable
partition 120 are determined, a measured displacement can be
calculated based on the first and second positions 119, 121 of the
movable partition 120. The measured displacement can represent a
variety of characteristics of pump operation. For example, in one
embodiment, the measured displacement can represent the actual
distance traveled by the movable partition 120. In another
exemplary embodiment, the measured displacement can represent the
volume of infusion fluid displaced by the movable partition 120.
After calculating the measured displacement, some measure of the
displacement can be compared to a pre-determined threshold value to
determine whether the infusion pump is malfunctioning 660. The
comparison of measured displacement to the predetermined threshold
value can take a variety of forms. For example, in one embodiment,
the actual measured displacement can be compared to the
pre-determined threshold value. In another embodiment, the square
of the actual measured displacement can be compared to the
pre-determined threshold value. In yet another exemplary
embodiment, comparing the measured displacement to the
pre-determined threshold value can include indicating a presence of
a malfunction if an absolute value of difference between the
measured displacement and the pre-determined threshold value is
greater than a predetermined threshold difference.
[0075] The pre-determined threshold value can represent a variety
of infusion pump operating parameters. For example, in one
exemplary embodiment shown in FIG. 16A, the pre-determined
threshold value can be a minimum acceptable value for the measured
displacement of the movable partition. In this embodiment,
comparing the measured displacement to the pre-determined threshold
value can further include indicating the presence of an occlusion
in the infusion pump 670a if the measured displacement is less than
the pre-determined threshold value 660a. In another exemplary
embodiment, shown in FIG. 16B, the pre-determined threshold value
can be a maximum acceptable value for the measured displacement of
the movable partition. In this embodiment, comparing the measured
displacement to the pre-determined threshold value can further
include indicating the presence of a fluid-loss condition 670b
(e.g., an infusion set disconnect or a leak) in the infusion pump
if the measured displacement is greater than the pre-determined
threshold value 660b. These pre-determined threshold values can be
selected by a user or determined by a processor or controller, as
described herein, depending upon a desired pump operation mode.
[0076] In one exemplary embodiment, the malfunction detection
method can include two pre-determined threshold values. In this
embodiment, one pre-determined threshold value can correspond to
occlusion detection and the other pre-determined threshold value
can correspond to fluid-loss detection. Thus, this embodiment can
provide simultaneous detection of both occlusions and fluid-loss
conditions. All or some of the malfunction detection steps
described above can be included in this embodiment.
[0077] As indicated above, it can be advantageous to operate the
infusion pump under a continuous activation/deactivation cycle.
Thus, in one exemplary embodiment of the malfunction detection
method disclosed herein, all or some of the above steps can be
repeated so as to monitor the infusion pump for malfunctions
throughout all or part of the activation/deactivation cycle. A
person skilled in the art will appreciate that the steps of the
method need not occur in any specific order. For example, the
infusion pump can be activated prior to determining a first
position of the movable partition. In an exemplary embodiment, the
above steps can be repeated as the movable partition 120 is
advanced through the infusion housing 116. In this embodiment, the
step of determining the first position of the movable partition 120
can include equating the first position of the movable partition
120 with a partition position corresponding with a previously
measured position of the movable partition. In yet another
embodiment, the method can include generating an alarm if the
presence of a malfunction is detected 680a, 680b.
[0078] A system for detecting a malfunction in an infusion pump is
also provided. As shown in FIG. 18, the system can include an
infusion pump 500 having a non-mechanically driven movable
partition 508 (e.g., hydraulically actuated) disposed therein, a
position sensor 504 disposed on the pump 500, a controller 502
associated with the pump 500, and a processor 506 associated with
the position sensor 504. In one exemplary embodiment, the infusion
pump can be an electrokinetic infusion pump. A variety of
configurations are available for the position sensor 504. For
example, the position sensor can be a magnetic sensor, an optical
sensor, or a linear variable differential transformer. A person
skilled in the art will appreciate that any sensor adapted to
measure position can be used with the malfunction detection
system.
[0079] The controller 502 of the malfunction detection system can
be adapted to operate the infusion pump 500 in an
activate/de-activate cycle. The cycle can include activating the
pump 500 for a first pre-determined amount of time to induce
movement of the movable partition 508 and de-activating the pump
500 for a second pre-determined amount of time. The controller 502
can also be adapted to cause a pressure build up in the infusion
pump 500 as the pump 500 is activated and de-activated for the
first and second pre-determined amounts of time. In one exemplary
embodiment, the controller 502 can be adapted to repeat the
activate/de-activate cycle while fluid is being delivered by the
infusion pump 500. A person skilled in the art will appreciate that
the controller 502 can be adapted to repeat the cycle as many times
are as necessary for the movable partition 508 to proceed through
the infusion pump 500. Furthermore, one or more separate components
or hardware control units can be combined as a "controller"
consistent with embodiments of the invention described herein. As
well, a "controller" can include memory units that are read-only or
capable of being overwritten to hold parameters such as selected
values or control parameters (e.g., the number of measured shot
amounts used in an averaging calculating, an expected shot amount,
the first and second pre-determined amounts of time, etc.). All
these variations, and others, are within the scope of the
disclosure of the present application.
[0080] The processor 506 of the malfunction detection system can be
adapted to calculate a measured displacement based on the first and
second positions of the movable partition 508 and to compare the
measured displacement with a pre-determined threshold value to
determine whether the infusion pump 500 is malfunctioning. The
processor 506 can also be adapted to lengthen or shorten the amount
of time that the pump 500 is de-activated to cause a slower or
faster build-up of pressure in the pump, respectively. In one
embodiment, the processor 506 can be adapted to indicate a presence
of a malfunction if an absolute value of difference between the
measured displacement and the pre-determined threshold value is
greater than a predetermined threshold difference. As indicated
above, the pre-determined threshold value can represent a variety
of infusion pump operating parameters. For example, in one
exemplary embodiment, the pre-determined threshold value can be a
minimum acceptable value for the measured displacement of the
movable partition. In this embodiment, the processor 506 can be
configured to indicate the presence of an occlusion in the infusion
pump if the measured displacement is less than the pre-determined
threshold value. In another exemplary embodiment, the
pre-determined threshold value can be a maximum acceptable value
for the measured displacement of the movable partition. In this
embodiment, the processor 506 can be configured to indicate the
presence of a fluid-loss condition in the infusion pump if the
measured displacement is greater than the pre-determined threshold
value. In one exemplary embodiment, the system can further include
an alarm adapted to receive a signal from the processor 506 and to
indicate the presence of a malfunction.
[0081] In another exemplary embodiment, the malfunction detection
system can include two pre-determined threshold values. One
pre-determined threshold value can correspond to occlusion
detection and the other pre-determined threshold value can
correspond to fluid-loss detection. Thus, this embodiment can
provide simultaneous detection of both occlusions and fluid-loss
conditions. In this embodiment, the processor can be configured to
indicate the presence of an occlusion if the calculated moving
average is less than a pre-determined occlusion threshold value as
well as indicate the presence of a fluid-loss condition if the
calculated moving average is greater than a pre-determined
fluid-loss threshold value. Additionally, in this embodiment, the
processor can include all the functionality as described above.
[0082] Furthermore, as with the controller 502 described above, one
or more separate components or hardware/software control units can
be combined as a "processor" consistent with embodiments of the
invention described herein. As well, a "processor" can include
memory units that are read-only or capable of being overwritten to
hold parameters such as selected or pre-determined values or
control parameters (e.g., the measured displacement, the expected
displacement, the first and second pre-determined amounts of time,
etc.). All these variations, and others, are within the scope of
the disclosure of the present application.
[0083] Malfunction Detection with Derivative Calculation
[0084] Another exemplary embodiment of a method for detecting a
malfunction in an infusion pump is illustrated in general form in
the flow chart provided in FIG. 17. The infusion pump can be
activated 710 for a first pre-determined amount of time to induce
movement of a non-mechanically driven movable partition of the pump
and to release a shot of fluid from the pump. In an exemplary
embodiment, the infusion pump can be an electrokinetic infusion
pump. The infusion pump can then be de-activated 710 for a second
pre-determined amount of time, and the position of the movable
partition can be determined 710 using any of the techniques
described above, for example, using a magnetic sensor. The above
steps can then be repeated for each of a plurality of instances
710. For example, the above steps can be repeated for at least two,
three, or five instances. A person skilled in the art will
appreciate that the above steps can be repeated for any number of
plurality of instances. Note that the position of the movable
partition need not be determined at the end of each
activate/de-activate cycle. In some embodiments, the
activate-de-activate cycle can be run for a selected number of
times before determining the position of the movable partition.
[0085] A derivative for each of the plurality of instances can then
be calculated 720. The derivative can be based on a change in
position of the movable partition with respect to a change in the
number of shots intended to be released. The change in position of
the movable partition can be represented by a variety of
parameters. For example, in one embodiment, the change in position
can represent the actual measured distance traveled by the movable
partition. In another embodiment, the change in position can be
represented by a change in sensor counts (e.g., a change in
position sensor output). Additionally, in an exemplary embodiment,
the derivative can be calculated using the last two known positions
of the movable partition for each of the plurality of instances. A
person skilled in the art will appreciate that the derivative can
be calculated using any two known positions of the movable
partition for each of the plurality of instances.
[0086] After calculating the derivative, a moving average can be
calculated using the calculated derivative values corresponding to
each of the plurality of instances 730. In an exemplary embodiment,
the moving average can represent the average of the last N
calculated derivative values over a specified period of time,
number of activate/de-activate cycles, or number of shots released.
In one embodiment, calculating the moving average can further
include multiplying the calculated derivative values by a weighting
factor. In another embodiment, the moving average can be an
arithmetic mean of derivative values. The calculated moving average
can then be compared with a pre-determined threshold value to
determine whether the infusion pump is malfunctioning 740.
[0087] The pre-determined threshold values can be selected by a
user or determined by a processor or controller, as described
herein, depending upon a desired pump operation mode. Moreover, the
pre-determined threshold values can represent a variety of infusion
pump operating parameters. For example, in one exemplary embodiment
shown in FIG. 17A, the pre-determined threshold value can represent
a minimum acceptable value for the change in position of the
movable partition with respect to the change in the number of shots
released 740a. In other words, if the change in position of the
movable partition with respect to the change in number of shots
released is less than the pre-determined threshold value, this can
indicate that the proper amount of infusion fluid is not being
released (i.e., too little infusion fluid is released) and that the
pump may be occluded. FIG. 13 illustrates the moving average A
(sensor counts/shot) over the course of a series of shots, wherein
the moving average A is an average of calculated derivative values
based on a change in position of a movable partition of a pump with
respect to a change in the number of shots released by the pump. As
shown in FIG. 13, the algorithm indicated a malfunction (i.e., an
occlusion) in the infusion pump after approximately 80 shots when
the moving average A dropped below threshold a which was set at 0.5
sensor counts/shot. In one exemplary embodiment, comparing the
calculated moving average to the pre-determined threshold value can
further include triggering a positive occlusion flag if the
calculated moving average is less than the pre-determined threshold
value 750a. Further, the occurrence of a positive occlusion flag
can also include generating an alarm signal if the calculated
moving average is less the first pre-determined threshold value
770a.
[0088] As indicated above, it is advantageous to operate the
infusion pump under a continuous activation/deactivation cycle.
Thus, in one exemplary embodiment of the malfunction detection
method disclosed herein, all or some of the above steps can be
repeated so as to monitor the infusion pump for malfunctions
throughout all or part of the activation/deactivation cycle. For
example, the above steps can be repeated as the movable partition
120 is advanced through the infusion housing 116. In this
embodiment, the step of comparing the calculated moving average can
include indicating the presence of an occlusion if the positive
occlusion flag occurs at least a pre-determined number of
consecutive times 760a. Some non-limiting examples of
pre-determined number of consecutive times include at least two,
three, or five consecutive positive occlusion flags. A person
skilled in the art will also appreciate that the pre-determined
number of consecutive times can be any number of times and
determination of which will depend on the infusion pump's
individual design and operating parameters.
[0089] As shown in FIG. 17B, the pre-determined threshold value can
also represent a maximum acceptable value for the change in
position of the movable partition with respect to the change in the
number of shots released 740b. In other words, if the change in
position of the movable partition with respect to the change in
number of shots released is greater than the pre-determined
threshold, this can indicate that the proper amount of infusion
fluid is not being released (i.e., too much infusion fluid is
released) and that there may be a fluid-loss condition in the
infusion set (e.g., an infusion set disconnect or a leak). FIG. 15
presents data from an electrokinetic infusion pump with closed loop
control having a fluid-loss condition in the infusion set. The
sensor counts and shot duration are shown as a function of time. As
shown in FIG. 15, a malfunction was detected at approximately 45
minutes into the experiment. At this time, the infusion set was
disconnect from the infusion reservoir, resulting in a lowering of
infusion pressure as the hydraulic resistance in the infusion line
was removed. This reduction of pressure results in a noticeable
sudden forward movement of the plunger. As a result of the
increased speed of the plunger, the control algorithm reduced the
shot duration. The fluid-loss condition is indicated by a decrease
in shot duration and an increase in sensor counts, as the closed
loop control attempted to correct the malfunctioning electrokinetic
infusion pump. As indicated in FIG. 15, the line was reconnected at
approximately 65 minutes into the experiment and it can be seen
that the control algorithm increased the shot duration to
accommodate the increased backpressure due to the re-attachment of
the infusion line. In one exemplary embodiment, comparing the
calculated moving average to the pre-determined threshold value can
further include triggering a positive fluid-loss flag if the
calculated moving average is greater than the pre-determined
threshold value 750b. Further, the occurrence of a positive
fluid-loss flag can also include generating an alarm signal if the
calculated moving average is greater the first pre-determined
threshold value 770b.
[0090] In one exemplary embodiment, the malfunction detection
method can include two pre-determined threshold values. In this
embodiment, one pre-determined threshold value can correspond to
occlusion detection and the other pre-determined threshold value
can correspond to fluid-loss (or set disconnect) detection. Thus,
this embodiment can provide simultaneous detection of both
occlusions and fluid-loss conditions. All or some of the
malfunction detection steps described above can be included in this
embodiment.
[0091] As indicated above, it is advantageous to operate the
infusion pump under a continuous activation/deactivation cycle.
Thus, similar to the occlusion detection method, all or some of the
above steps can be repeated so as to monitor the infusion pump for
fluid-loss conditions throughout all or part of the
activation/deactivation cycle. As with the occlusion detection
method, the step of comparing the calculated moving average can
include indicating the presence of a fluid-loss condition if the
positive fluid-loss flag occurs at least a pre-determined number of
consecutive times 760b. Some non-limiting examples of
pre-determined number of consecutive times include at least two,
three, or five consecutive positive fluid-loss flags. One skilled
in the art will appreciate that the pre-determined number of
consecutive times need not be the same for indicating the presence
of an occlusion and/or a fluid-loss condition. For example, the
presence of an occlusion can be indicated if the positive occlusion
flag occurs at least three times, and the presence of a fluid-loss
condition can be indicated if the positive fluid-loss flag occurs
at least two times. A person skilled in the art will also
appreciate that the methods disclosed herein for detecting
occlusions and/or fluid-loss conditions can be performed
independent of each other or in conjunction.
[0092] A system associated with the above method for detecting a
malfunction in an infusion pump is also provided. The system can
include an infusion pump 500 having a non-mechanically driven
movable partition 508 disposed therein, a position sensor 504
disposed on the pump 500, a controller 502 associated with the pump
500, and a processor 506 associated with the position sensor 504.
In one exemplary embodiment, the infusion pump can be an
electrokinetic infusion pump. A variety of configurations are
available for the position sensor 504. For example, the position
sensor 504 can be a magnetic sensor, an optical sensor, or a linear
variable differential transformer. A person skilled in the art will
appreciate that any sensor adapted to measure position can be used
with the malfunction detection system.
[0093] The controller 502 of the malfunction detection system can
be adapted to operate the infusion pump 500 in an
activate/de-activate cycle. The cycle can include activating the
pump for a first pre-determined amount of time to induce movement
of the movable partition and release a shot of fluid and
de-activating the pump for a second pre-determined amount of time.
The controller 502 can also be adapted to cause a pressure build up
in the infusion pump 500 as the pump is activated and de-activated
for the first and second pre-determined amounts of time. In one
exemplary embodiment, the controller 502 can be adapted to repeat
the activate/de-activate cycle while fluid is being delivered by
the infusion pump 500. A person skilled in the art will appreciate
that the controller 502 can be adapted to repeat the cycle as many
times are as necessary for the movable partition 508 to proceed
through the infusion pump 500.
[0094] The processor 506 of the malfunction detection system can be
adapted to perform a series of functions after each
activate/de-activate cycle. For example, the processor 506 can be
adapted to calculate a derivative based on a change in position of
the movable partition 508 with respect to a change in the number of
shots released. The processor 506 can also be adapted to calculate
a moving average from a plurality of the calculated derivative
values. In one exemplary embodiment, calculating the moving average
can further include multiplying the calculated derivative values by
a weighting factor. The processor 506 can also be configured to
calculate the moving average based upon calculated derivatives from
at least a last three cycles. In another embodiment, the processor
506 can be configured to calculate the moving average based upon
calculated derivatives from a last fives cycles. Additionally, the
processor 506 can be adapted to determine whether the pump 500 is
malfunctioning by comparing the calculated moving average to a
pre-determined threshold value. The pre-determined threshold value
can represent a variety of infusion pump operating parameters. For
example, in one exemplary embodiment, the pre-determined threshold
value can represent a minimum acceptable value for the change in
position of the movable partition with respect to the change in the
number of shots released. In this embodiment, the processor 506 can
be configured to provide a positive occlusion flag if the
calculated moving average is less than the pre-determined threshold
value. In one embodiment, the processor 506 can be further
configured to produce an occlusion detection signal if the positive
occlusion flag is produced after each of at least a pre-determined
number of consecutive cycles. For example, in some exemplary
embodiments, the pre-determined number of cycles can be at least
one, two, three, or five. FIG. 14 illustrates the number of false
alarms (i.e., the number of false indications of an occlusion) for
various values of pre-determined threshold values which represented
the minimum acceptable value for the change in position of the
movable partition with respect to the change in the number of shots
released. The processor 506 used in the simulation was configured
to produce an occlusion detection signal if a positive occlusion
flag was produced after each or at least one, two, or three
consecutive cycles. As shown in FIG. 14, the greatest number of
false alarms occurred when the processor 506 was configured to
produce an occlusion detection signal if a positive occlusion flag
was produced after one consecutive cycle. The least number of false
alarms occurred when the processor 506 was configured to produce an
occlusion detection signal if a positive occlusion flag was
produced after three consecutive cycles. Thus, increasing the
number of consecutive positive occlusion flag cycles required
before indicating the presence of an occlusion, decreases the
number of false alarms. However, increasing the number of
consecutive positive occlusion flag cycles required also increases
the amount of time it takes to detect an occlusion.
[0095] In another exemplary embodiment, the pre-determined
threshold value can represent a maximum acceptable value for the
change in position of the movable partition with respect to the
change in the number of shots released. In this embodiment, the
processor 506 can be configured to provide a positive fluid-loss
flag if the calculated moving average is greater than the
pre-determined threshold value. As with the occlusion detection
signal, the processor 506 can be further configured to produce an
fluid-loss detection signal if the positive fluid-loss flag is
produced after each of at least a pre-determined number of
consecutive cycles. As indicated above, one skilled in the art will
appreciate that the pre-determined number of consecutive times need
not be the same for indicating the presence of an occlusion and/or
a fluid-loss condition. For example, the presence of an occlusion
can be indicated if the positive occlusion flag occurs at least
three times, and the presence of a fluid-loss condition can be
indicated if the positive fluid-loss flag occurs at least two
times. A person skilled in the art will also appreciate that the
pre-determined number of consecutive times can be any number of
times and determination of which will depend on the infusion pump's
individual design and operating parameters. Additionally, in one
exemplary embodiment, the system can further include an alarm
coupled to the processor and adapted to produce a signal indicating
a malfunction (e.g. an occlusion and/or a fluid-loss condition)
upon activation.
[0096] In one exemplary embodiment, the malfunction detection
method can include two pre-determined threshold values. One
pre-determined threshold value can correspond to occlusion
detection and the other pre-determined threshold value can
correspond to fluid-loss detection. Thus, this embodiment can
provide simultaneous detection of both occlusions and fluid-loss
conditions. In this embodiment, the processor can be configured to
provide a positive occlusion flag if the calculated moving average
is less than a pre-determined occlusion threshold value as well as
provide a positive fluid-loss flag if the calculated moving average
is greater than a pre-determined fluid-loss threshold value.
Further, in this embodiment, the processor can include all the
functionality as described above.
EXAMPLES
[0097] The following examples are provided to illustrate some
aspects of the present application. The examples, however, are not
intended to limit the scope of any embodiment of the invention.
Example 1
Basal and Bolus Liquid Delivery
[0098] Referring to FIG. 7, using an electrokinetic infusion pump
with closed loop control 100 basal and bolus infusion liquid
delivery rates were determined. In basal infusion, small volumes
are dispensed at high frequency. In bolus infusion, large volumes
are dispensed at a low frequency. Basal and bolus infusion liquid
delivery rates were determined by applying voltage to
electrokinetic engine 102 for a period of time (referred to as the
pump on time), then switching the voltage off for a period of time
(referred to as the pump off time). The sum of pump on time and
pump off time is referred to as cycle time in this example. The
mass of infusion liquid pumped during each cycle time (referred to
as the shot size) was determined with a Mettler Toledo AX205
electronic balance. The shot size was determined repeatedly, using
the same pump on time and the same cycle time, giving an indication
of shot size repeatability. Using the density of water (about 1
gram per cubic centimeter), the shot size volume was derived from
the mass of infusion liquid pumped during each cycle time.
[0099] Electrokinetic engine 102 was connected to infusion module
104 using connection tubing 244. Connection tubing 244 was rigid
PEEK tubing with an inside diameter of 0.040'', an outside diameter
of 0.063'', and a length of approximately 3''. A similar piece of
PEEK tubing, approximately 24'' long, was connected to infusion
reservoir outlet 123 on one end, and to glass capillary tubing on
the other end. The glass capillary tubing had an inside diameter of
0.021'', an outside diameter of 0.026'', and a length of about 6''.
The end of the glass capillary tubing, which was not connected to
infusion reservoir outlet 123, was inserted into a small vial being
weighed by the Mettler Toledo AX205 electronic balance. A small
amount of water was placed in the bottom of the small vial,
covering the end of the glass capillary tubing, and a drop of oil
was placed on top of the water in the bottom of the small vial to
reduce evaporation of the water. Electrokinetic engine 102 was also
connected to a vented electrokinetic solution reservoir (not shown
in FIG. 7) that provided electrokinetic solution to electrokinetic
engine 102. Electrokinetic engine 102, vented electrokinetic
solution reservoir, infusion module 104, connection tubing 244, the
glass capillary tubing, and the Mettler Toledo AX205 electronic
balance, were placed inside a temperature-controlled box, held to
+/-1.degree. C., to eliminate measurement errors associated with
temperature variations. The temperature-controlled box was placed
on top of a marble table to reduce errors from vibration. A
personal computer running LabView software controlled
electrokinetic infusion pump with closed loop control 100 and
collected data from the Mettler Toledo AX205 electronic
balance.
[0100] To determine basal delivery of infusion liquid,
electrokinetic engine 102 was connected to infusion module 104 with
connection tubing 244 and driven with a potential of 75V. At 75V,
electrokinetic engine 102 delivered electrokinetic solution to
infusion module 104 at a rate of approximately 15
microliters/minute. Electrokinetic engine 102 was run with an on
time of approximately 2 seconds and an off time of approximately 58
seconds, resulting in a cycle time of 60 seconds and a shot size of
approximately 0.5 microliters. The on-time of electrokinetic engine
102 was adjusted, based upon input from magnetostrictive waveguide
177 and position sensor control circuit 160, which ran a closed
loop control algorithm in accord with the description of FIG. 2.
For each cycle of basal delivery, the position of moveable
permanent magnet 149 was determined. If moveable permanent magnet
149 did not move enough, the on time for the next cycle of basal
delivery was increased. If moveable permanent magnet 149 moved too
much, the on time for the next cycle of basal delivery was
decreased. The determination of position of moveable permanent
magnet 149, and any necessary adjustments to on time, was repeated
for every cycle of basal delivery.
[0101] To determine bolus delivery of infusion liquid,
electrokinetic engine 102 was connected to infusion module 104 with
connection tubing 244 and driven with a potential of 75V. Once
again, at 75V electrokinetic engine 102 delivered electrokinetic
solution to infusion module 104 at a rate of approximately 15
microliters/minute. Electrokinetic engine 102 was run with an on
time of approximately 120 seconds and an off time of approximately
120 seconds, resulting in a cycle time of 4 minutes and a shot size
of approximately 30 microliters. For each cycle of bolus delivery,
the position of moveable permanent magnet 149 was determined while
the electrokinetic engine 102 was on. Once moveable permanent
magnet 149 moved the desired amount, electrokinetic engine 102 was
turned off. The position of moveable permanent magnet 149 was used
to control on time of electrokinetic engine 102 for every cycle of
bolus delivery.
[0102] Basal and bolus delivery of infusion liquid were alternated,
as follows. Thirty cycles of basal delivery was followed by one
cycle of bolus delivery. Then, thirty-seven cycles of basal
delivery, was followed by one cycle of bolus delivery. Finally,
thirty-eight cycles of basal delivery was followed by a one cycle
of bolus delivery and forty-nine additional cycles of basal
delivery. FIG. 8 is a graph showing measured shot size as a
function of time, for alternating basal delivery 243 and bolus
delivery 245, as outlined above. In basal mode, the average shot
size was about 0.5 microliters with a standard deviation of less
than 2%.
Example 2
Occlusion Detection with Closed Loop Control
[0103] FIG. 9 is a flow diagram illustrating a method of detecting
occlusions in an electrokinetic infusion pump with closed loop
control 100 according to an embodiment of the present invention.
With reference to FIG. 9, and FIGS. 1 through 8, closed loop
controller 105 starts with a normal status 246. In the next step,
closed loop controller 105 determines position 250 of moveable
partition 120. After determining the position 250 of moveable
partition 120, closed loop controller 105 waits before dose 252.
During this time, the pressure in electrokinetic infusion pump 103
decreases. After waiting before dose 252, a fixed volume is dosed
254. This is accomplished by activating the electrokinetic engine
102. As a result of dosing a fixed volume 254 (electrokinetic
engine on time), the pressure in electrokinetic infusion pump 103
increases as a function of time, as illustrated in FIG. 10.
Multiple graphs are illustrated in FIG. 10, showing the effect of
time between shots (electrokinetic engine off time) on pressure in
electrokinetic infusion pump 103. Waiting 1 minute between shots
results in a rapid build up of pressure. Waiting 5 minutes between
shots results in a longer time to build pressure. The rate at which
pressure builds is the same in each graph, but the starting
pressure decreases as a function of time between shots, and
therefore results in longer times to build pressure. Each graph
eventually reaches the same approximate pressure, in this case
about 3.2 psi. This is the pressure needed to displace moveable
partition 120. Returning to FIG. 9, after dosing a fixed amount
254, and waiting after dose 256 (during which time the pressure in
electrokinetic infusion pump 103 increases), the change in position
258 of moveable partition 120 is determined. The position of
moveable partition 120 can be determined using a variety of
techniques, as mentioned previously. After determining the change
in position 258 of moveable partition 120, closed loop controller
105 determines if moveable partition 120 has moved as expected 260,
or if it has not moved as expected 264. If moveable partition 120
has moved as expected 260, then no occlusion 262 has occurred, and
the closed loop controller 105 returns to normal status 246. If the
moveable partition 120 has not moved as expected 264, then an
occlusion 266 has occurred, and the closed loop controller 105
enters an alarm status 248. FIG. 11 is a graph illustrating the
position of moveable partition 120 as a function of time when an
occlusion occurs in an electrokinetic infusion pump with closed
loop control 100, according to the embodiment described in the
previous example (i.e., running with a series of on/off times using
feedback control). As can be seen in FIG. 11, after about 70
minutes the rate at which moveable partition 120 moves as a
function of time suddenly decreases in region 250. This indicates
that an occlusion has occurred, blocking the movement of moveable
partition 120.
[0104] One skilled in the art will appreciate further features and
advantages of the invention based on the above-described
embodiments. Accordingly, the invention is not to be limited by
what has been particularly shown and described, except as indicated
by the appended claims. All publications and references cited
herein are expressly incorporated herein by reference in their
entirety.
* * * * *